Cylinder unit for an air-cooled two-stroke-cycle engine

ABSTRACT

A cylinder unit for an air-cooled two-stroke-cycle engine, especially for motorcycles, whose cylinder and cylinder head are equipped with projecting cooling ribs whereby the cooling ribs of the cylinder are inclined to the cylinder axis transversely to the approach flow direction of the cooling air in such a manner that the spacings of these cooling ribs increase from the inside toward the outside, i.e., from the cooling rib bottom toward the free edges thereof.

United States Patent Schier 1 Jan. 1, 1974 [54] CYLINDER UNIT FOR AN AIR-COOLED 2,184,345 12/1939 Hersey 123/4169 X TWO STROKE CYCLE ENGINE 2,595,050 4/1952 Bronandcr... 123/4169 2,766,741 10/1956 Flatz et a1. 123/4167 [75] Inventor: Gunther Schier, Pfaffingen,

Germany FOREIGN PATENTS OR APPLICATIONS 230,281 9/1956 Australia 123/4169 {73] Assigne Fahrzeugfabnk GmbH, 1,052,386 9/1953 France 123141.69 Pfa fing Germany 201,354 8/1923 Great Britain 123/4l.69 944,264 12/1963 Great Britain.. 123/41.69 [22] .1972 291,310 9/1953 Switzerland 123141.69 [21] Appl. No.: 306,876 7 Primary Examiner-Al Lawrence Smith [30] Foreign Application Priority Data Attorney-P3111 M. Craig, Jr. et a1.

Nov. 16, 1971 Germanyvmj. P 21 56 754.4 ABSTRACT 52 us. c1. l23/41.69 A cy1inder unit for an air-cooled two-stroke-cycle [51] 1111. C1 F021 l/06, F02f 1/30 give. especially or torcycles, whose cylinder and 581 Field of Search 123/4156, 41.6, cylinder head are equipped with Pmiecting 123/4167 41'69 ribs whereby the cooling ribs of the cylinder are inclined to the cylinder axis transversely to the approach [56] References Cited flow directionof the cooling air in such a manner that v UNITED STATES PATENTS the spacings of these cooling ribs increase from the inside toward the outside, i.e., from the cooling rib bot- 882.133 15/13; 321122; 123 4169 x tom toward the free edgesthereof r1 n... 2,162,514 6/1939 Meyer 123/4169 17 Claims, 3 Drawing Figures 1I 10 ll 70 CYLINDER UNIT FOR AN AIR-COOLED TWO-STROKE-CYCLE ENGINE The present invention relates to a cylinder unit for an air-cooled two-stroke-cycle engine, especially for motorcycles whose cylinder and cylinder head are equipped with projecting cooling ribs.

With such cylinder units, the cooling ribs of the cylinder are constructed as rings which are arranged parallel to one another in planes disposed perpendicularly to the cylinder axis. The cooling ribs are necessary since the air has a relatively low coefficient of thermal conductivity and thus a sufficient cooling can be assured only by way of an enlargement of the surface which is available for that purpose. The construction of such cooling ribs therefore requires an increased care especially with high power engines.

In the prior art constructions of the cooling ribs, their length and their spacing have to be selected at a favorable relationship to one another as otherwise the cooling air flow no longer reaches the bottom of the ribs. A difficulty exists precisely in that connection with these cylinder units of the aforementioned type insofar as it is not simple to so conduct the cooling air flow produced for the most part exclusively by the dynamic air stream that it reaches the rib bottom to the greatest possible extent in all areas and not only on the approach-flow side,.i.e., on the side exposed to the onflowing air.

The present invention is therefore concenred with the task to provide a cylinder of a two-stroke-cycle engine of the aforementioned type which enables an advantageous cooling air flow. The present invention essentially consists in that the cooling ribs of the cylinder are inclined to the cylinder axis transversely with respect to the on-flow direction of the cooling air in such a manner that the spacings of the cooling ribs increase from the inside toward the outside, i.e., from the bottoms toward the free ends thereof. As a result thereof, flow cross sections for the cooling air are created which assure that the cooling air also reaches the rib bottom.

In one structurally advantageous embodiment of the present invention, provision is made that the cooling ribs of the cylinder extend, as viewed in the approach flow direction, up to the outer coutour of the cylinder perpendicularly to the cylinder axis and parallel to one another and adjacent thereto are angularly bent off in the upward or downward direction. Such a cylinder can be manufactured by the use of the same methods as are utilized also in the manufacture of the prior art cylinders. It is thereby appropriate if the angularly bent portions of the cooling ribs of the cylinder extend approximately radially with respect to an axis disposed in the approach flow direction.

According to a further feature of the present invention, provision is made that the upper cooling ribs of the cylinder are angularly bent up above the separating plane and toward the cylinder head whose outer cooling ribs are directed obliquely upwardly. With this construction of the present invention, the improved cooling of the cylinder is realized, to a certain extent, to the detriment of the cooling of the cylinder head. This, however, has the surprising advantage that without increasing the temperature of the cylinder, a higher combustion end temperature can be achieved which in turn leads to an increased engine output.

An advantageous construction of the present invention results in that the cooling ribs of the cylinder head which extend in the approach-flow direction of the cooling air and which are arranged fan-like, extend approximately radially to the axis of the angularly bent portions of the cooling ribs of the cylinder. A uniform distribution of the cooling ribs over the cylinder and the cylinder head results therefrom which leads to a uniform distribution of the cooling air flow. Additionally, such an engine receives a pleasing external appearance. It is structurally favorable with this embodiment if the common axis lies approximately at half the height of the cylinder;

For reasons of rigidity and strength, it is appropriate if the cooling ribs are connected with each other pairwise within the area of their ends by means of webs. Vibration appearances and phenomena can be farreachingly excluded as a result thereof or can be controlled at least in their effects. It is thereby favorable if the webs constructed as guide means directed inwardly toward the cylinder. It becomes possible by these measures to deflect the cooling air flow additionally toward the rib bottom which can be of advantage especially for the area of the cylinder oposite the approach-flow direction.

The accommodation of the cooling ribs of the cylinder according to the present invention permits an enlargement of the cooling ribs without having to increase the installed width whereas simultaneously the guidance of the air flow is influenced in an advantageous manner. It is favorable thereby if the cooling ribs of the cylinder, as viewed in plan view, have an approximately rectangular configuration.

Accordingly, it is an object of the present inventionto provide a cylinder unit for an air-cooled two-strokecycle internal combustion engine which avoids by simple means the aforementioned shortcomings and drawbacks encountered in the prior art.

Another object of the present invention resides in a cylinder unit for an air cooled two-cycle engine which effectively increases the cooling effect, necessary for high power engines.

A further object of the present invention resides in a cylinder unit for an air-cooled two-stroke-cycle engine which assures that the cooling air flow reaches the bottom of the ribs in all areas of the cylinder and cylinder head.

A still further object of the present invention resides in a cylinder and cylinder head unit of the aforementioned type which improves the cooling effect by simple means, permitting continued use of hitherto existing manufacturing methods.

Another object of the present invention resides in a cylinder unit for an air-cooled two-cycle engine which permits higher combustion end temperatures and therewith higher engine outputs without increasing the temperature of the cylinder.

A further object of the present invention resides in an internal combustion engine of the type described above which leads to a more uniform distribution of the cooling air flow, avoids vibrational phenomena and permits an increase in the cooling rib surfaces without requiring an increase in the overall dimensions of the engine.

These further objects, features, and advantages of the present invention will become more apparent from he following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention, and wherein:

FIG. 1 is a view of a cylinder in accordance with the present invention, which is illustrated with one-half thereof in elevational view and with one-half thereof in axial cross-sectional view and which is equipped with a cylinder head shown in axial cross section;

FIG. 2 is a cross-sectional view through the cylinder and cylinder head taken along the line II-II of FIG. 1; and

FIG. 3 is a partial plan view on one cylinder half with a removed cylinder head.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, the illustrated cylinder of a twostroke-cycle engine is used with preference in highpower two-wheel vehicles, especially with so-called Moto-Cross vehicles. It will be so arranged that the cylinder axis extends vertically or slightly inclined in the driving direction. In such a vehicle, the dynamic air flow serves as cooling air stream. This means that the cylinder or cylinders have to be so arranged that a favorable cooling air flow is achieved.

The illustrated two-stroke-cycle engine includes a cylinder generally designated by reference numeral 1 which is closed off in the upward direction by means of a cylinder head generally designated by reference numeral 2. The cylinder land the cylinder head 2 are made as cast parts from a light metal alloy of conventional type. A liner (not shown) of gray cast iron is provided as running surface of a piston reciprocating within the cylinder; theliner is shrunk into the cylinder 1 and projects upwardly with a collar above the cylinder 1. The cylinder head 2 is centered by means of a recess 3 on a gray cast liner and is secured at the cylinder 1 by means of cylinder head bolts (not shown).

The cylinder 1 includes an exhaust channel 6 point ing in the driving direction, i.e., opposite the approachflow direction of the cooling air indicated by arrow 4. A slightly inclined inlet channel is arranged diammetrically opposite the exhaust channel 6, through disposed slightly lower. Subdividecl overflow channels 7 for the engine operating with a Schnurle-reverse scavenging are provided offset by approximately 90 to the inlet channel 5 and to the exhaust channel 6.

Cooling ribs 8 are integrally cast-on externally at the cylinder 1 in regular intervals. The cooling ribs 8 extend within the forward and rearward area of the cylinder 1, i.e., on the side facing the cooling air flow 4 and on the side opposite the cooling air flow 4, parallel to one another and a mutual spacings which are regular and remain the same. The surrounding cooling ribs 8 which are made longer on the approach-flow side are interrupted, respectively, within the area of the inlet connection 5 and of the exhaust channel 6 in order to be able to connect a suction pipe and an exhaust line, respectively.

Within the remaining area, i.e., in the area laterally projecting beyond the'contour of the cylinder 1, as viewed in the approach flow direction, the ribs 8 are arranged inclined with respect to the cylinder axis in such a manner that the spacing between the cooling ribs 8 increases from the rib bottom toward the outside. For that purpose, the cooling ribs 8 are angularly bent in their lateral area in such a manner that a bending line (FIG. 3) extends approximately tangentially to the outside of cylinder 1. The angularly bent portions of the cooling ribs 8 are arranged fan-like, i.e., they extend approximately radially to an axis extending in the approach flow direction 4. This axis or this area is disposed approximately at half the height of the cylinder 1 so that the cooling ribs 8 disposed at the height of the exhaust channel 6 are disposed in planes extending essentially perpendicularly to the cylinder axis. The cooling ribs 8 disposed thereabove rise at ever-larger angles with an increase in the distance whereas the cooling ribs 8 disposed therebelow are inclined downwardly at ever-increasing angle with an increase in the distance.

The cooling ribs 8 have an approximately rectangular configuration as viewed in plan view as illustrated in FIG. 3. They are so constructed that they terminate on each side in lateral planes parallel to the approach flow direction 4 and perpendicular to the cylinder axis. Shortly in front of their free ends, the cooling ribs 8 are connected with each other pairwise by means of webs 9 within the area of a vertical center plane. As illustrated in dash line in FIG. 3, these webs 9 can be constructed as guide means directed toward the rear area of the cylinder 1 opposite the approach-flow direction 4 in that they receive an appropriate inclination or cur vature directed toward this area.

As can be seen from FIG. 1, the two upper cooling ribs 8 of the cylinder 1 projectupwardly above the separating plane between the cylinder 1 and the cylinder head 2. The cylinder head 2 is equipped with cooling ribs 10 (FIG. 1) which extend in the approach-flow direetion 4 of the cooling air. Their length corresponds approximately to the length of the cooling ribs 8 of the cylinder 1 in this direction. The cooling ribs 10 of the cylinder head 2 extend approximately radially to a common axis which coincides approximately with the common axis of the cooling ribs 8 of the cylinder 1.

Since the upper cooling ribs 8 of the cylinder 1 project above the separating plane to the cylinder head 2, also the lower cooling ribs 10 of the cylinder head 2 are already inclined upwardly. A certain reduction of the cooling effect of the cylinder head 2 is accepted thereby compared to the known types of construction which are also equipped with fan-like cooling ribs whereby, however, the lowermost cooling ribs are disposed parallel to the separating plane. This reduction of the cooling of the cylinder head 2, in contrast thereto, enables an enhanced cooling of the cylinder 1. It is altogether achieved in this manner that the combustion end temperature can be raised without the fact that the cylinder and the piston reciprocating therein on the inside of a liner are loaded more strongly. An increased thermal load of the cylinder head 2 does not become noticeable in a disturbing or impairing manner since its mechanical loads are relatively slight in comparison to the cylinder 1 and especially to the piston. The increase of the combustion end temperature permits directly an increase of the output.

The two outer cooling ribs 10 of the cylinder head 2 are connected with each other by webs 11. The two upper cooling ribs 8 of the cylinder 1 and the cooling ribs 10 of the cylinder head 2 are delimited by an approximately cylindrical surface.

While I have shown and described only one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art, and I therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

What I claim is:

1. A cylinder unit for an air-cooled two-cycle engine whose cylinder means and cylinder head means are equipped with projecting cooling rib means, characterized in that the cooling rib means of the cylinder means are inclined with respect to the cylinder axis transversely to the approach flow direction of the cooling air in such a manner that the spacings of the cooling rib means increase from the inside toward the outside.

2. A cylinder unit according to claim 1, characterized in that the two-cycle engine is installed in a motorcycle.

3. A cylinder unit according to claim 1, characterized in that the cooling rib means of the cylinder means extend, as viewed in the approach flow direction, substantially perpendicularly to the cylinder axis and parallel to one another up to the outer contour of the cylinder means and adjacent thereto are angularly bent upwardly or downwardly, respectively.

4. A cylinder unit according to claim 3, characterized in that the angularly bent portions of the cooling rib means of the cylinder means extend approximately radially to an axis disposed substantially in the approach flow direction.

5. A cylinder unit according to claim 4, characterized in that the upper cooling rib means of the cylinder means are angularly bent off upwardly beyond the separating plane with respect to the cylinder head means, and in that the outer cooling rib means of the cylinder head means are directed obliquely upwardly.

6. A cylinder unit according to claim 5, characterized in that the cooling rib means of the cylinder head means which extend in theapproach flow direction of the cooling air and which are arranged fan-like, extend approximately radially to the axis of the angularly bent portions of the cooling rib means of the cylinder means.

7. A cylinder unit according to claim 6, characterized in that the common axis is disposed approximately at half the height of the cylinder means.

8. A cylinder unit according to claim 7, characterized in that the cooling rib means are connected with each other pairwise within the area of their ends by web means.

9. A cylinder unit according to claim 8, characterized in that the web means are constructed as guide means directed inwardly toward the cylinder means.

10. A cylinder unit according to claim 9, characterized in that the cooling rib means of the cylinder means have an approximately rectangular configuration as viewed in plan view.

11. A cylinder unit according to claim 1, characterized in that the upper cooling rib means of the cylinder means are angularly bent off upwardly beyond the separating plane with respect to the cylinder head means, and in that the outer cooling rib means of the cylinder head means are directed obliquely upwardly.

12. A cylinder unit according to claim 1 1, characterized in that the cooling rib means of the cylinder head means which extend in the approach flow direction of the cooling air and which are arranged fan-like, extend approximately radially to an axis of the angularly bent portions of the cooling rib means of the cylinder means.

13. A cylinder unit according to claim 12, characterized in that the common axis is disposed approximately at half the height of the cylinder means.

14. A cylinder unit according to claim 1, characterized in that the cooling rib means are connected with each other within the area of their ends by web means.

15. A cylinder unit according to claim 14, characterized in that the web means are constructed as guide means directed inwardly toward the cylinder means.

16. A cylinder unit according to claim 1, characterized in that the cooling rib means of the cylinder means have an approximately rectangular configuration as viewed in plan view.

17. A cylinder unit according to claim 4, characterized in that the axis is disposed approximately at half the height of the cylinder means. 

1. A cylinder unit for an air-cooled two-cycle engine whose cylinder means and cylinder head means are equipped with projecting cooling rib means, characterized in that the cooling rib means of the cylinder means are inclined with respect to the cylinder axis transversely to the approach flow direction of the cooling air in such a manner that the spacings of the cooling rib means increase from the inside toward the outside.
 2. A cylinder unit according to claim 1, characterized in that the two-cycle engine is installed in a motorcycle.
 3. A cylinder unit according to claim 1, characterized in that the cooling rib means of the cylinder means extend, as viewed in the approach flow direction, substantially perpendicularly to the cylinder axis and Parallel to one another up to the outer contour of the cylinder means and adjacent thereto are angularly bent upwardly or downwardly, respectively.
 4. A cylinder unit according to claim 3, characterized in that the angularly bent portions of the cooling rib means of the cylinder means extend approximately radially to an axis disposed substantially in the approach flow direction.
 5. A cylinder unit according to claim 4, characterized in that the upper cooling rib means of the cylinder means are angularly bent off upwardly beyond the separating plane with respect to the cylinder head means, and in that the outer cooling rib means of the cylinder head means are directed obliquely upwardly.
 6. A cylinder unit according to claim 5, characterized in that the cooling rib means of the cylinder head means which extend in the approach flow direction of the cooling air and which are arranged fan-like, extend approximately radially to the axis of the angularly bent portions of the cooling rib means of the cylinder means.
 7. A cylinder unit according to claim 6, characterized in that the common axis is disposed approximately at half the height of the cylinder means.
 8. A cylinder unit according to claim 7, characterized in that the cooling rib means are connected with each other pairwise within the area of their ends by web means.
 9. A cylinder unit according to claim 8, characterized in that the web means are constructed as guide means directed inwardly toward the cylinder means.
 10. A cylinder unit according to claim 9, characterized in that the cooling rib means of the cylinder means have an approximately rectangular configuration as viewed in plan view.
 11. A cylinder unit according to claim 1, characterized in that the upper cooling rib means of the cylinder means are angularly bent off upwardly beyond the separating plane with respect to the cylinder head means, and in that the outer cooling rib means of the cylinder head means are directed obliquely upwardly.
 12. A cylinder unit according to claim 11, characterized in that the cooling rib means of the cylinder head means which extend in the approach flow direction of the cooling air and which are arranged fan-like, extend approximately radially to an axis of the angularly bent portions of the cooling rib means of the cylinder means.
 13. A cylinder unit according to claim 12, characterized in that the common axis is disposed approximately at half the height of the cylinder means.
 14. A cylinder unit according to claim 1, characterized in that the cooling rib means are connected with each other within the area of their ends by web means.
 15. A cylinder unit according to claim 14, characterized in that the web means are constructed as guide means directed inwardly toward the cylinder means.
 16. A cylinder unit according to claim 1, characterized in that the cooling rib means of the cylinder means have an approximately rectangular configuration as viewed in plan view.
 17. A cylinder unit according to claim 4, characterized in that the axis is disposed approximately at half the height of the cylinder means. 